I cannot send texts to some of my contacts via iMessage
I have anew iPad Pro. I cannot send messages to some of my contacts. I get a error message when I tap on their name that they are not registered. I also have an iPhone and I can send messages to those same people from it. I also am not receiving messages from them on my iPad although I am receiving them on my iPhone. I have checked all my settings and they seem to be correct.
iPad Pro Wi-Fi, iOS 10.3.3